Teretia megalembryon is a species of sea snail, a marine gastropod mollusk in the family Raphitomidae.

The minute, solid shell is whitish, except for the yellowish brown protoconch.

The suture is distinct, constricted, with a fringe of minute axial wrinkles on the fasciole in front of it.

The spiral sculpture consists of (on the penultimate whorl 6 and on the body whorl about 10) fine, equal and equally distributed low threads with narrower interspaces, covering the whole shell except the anal fasciole.

[2][3] This species occurs in the Atlantic Ocean off the Azores and off Georgia, USA.